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Methanosarcina barkeri
About: Methanosarcina barkeri is a research topic. Over the lifetime, 703 publications have been published within this topic receiving 32151 citations.
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TL;DR: It is reported here that the enzyme from Methanobacterium thermoautotrophicum and Methanosarcina barkeri catalyzes the reduction of CoM‐S‐S-HTP with reduced viologen dyes and, in the reverse direction, the oxidation of H‐S•CoM plus H‐ S‐HTP to the heterodisulfide by methylene blue.
47 citations
TL;DR: The structures of core lipids of methanogenic archaebacterium, Methanosarcina barkeri are quite different from those previously reported by De Rosa et al.
46 citations
TL;DR: The first enzyme of pyruVate catabolism, pyruvate oxidoreductase, which catalyzes oxidation of pyrivate to acetyl-CoA was purified about 90-fold to apparent electrophoretic homogeneity and has an alpha beta gamma delta structure.
Abstract: Methanosarcina barkeri (strain Fusaro) was grown on pyruvate as methanogenic substrate [Bock, A. K., Prieger-Kraft, A. & Schonheit, P. (1994) Arch. Microbiol. 161, 33–46]. The first enzyme of pyruvate catabolism, pyruvate oxidoreductase, which catalyzes oxidation of pyruvate to acetyl-CoA was purified about 90-fold to apparent electrophoretic homogeneity. The purified enzyme catalyzed the CoA-dependent oxidation of pyruvate with ferredoxin as an electron acceptor which defines the enzyme as a pyruvate: ferredoxin oxidoreductase. The deazaflavin, coenzyme F420, which has been proposed to be the physiological electron acceptor of pyruvate oxidoreductase in methanogens, was not reduced by the purified enzyme. In addition to ferredoxin and viologen dyes, flavin nucleotides served as electron acceptors. Pyruvate: ferredoxin oxidoreductase also catalyzed the oxidation of 2-oxobutyrate but not the oxidation of 2-oxoglutarate, indolepyruvate, phenylpyruvate, glyoxylate, 3-hydroxypyruvate and oxaloacetate. The apparent Km values of pyruvate: ferredoxin oxidoreductase were 70 μM for pyruvate, 6 μM for CoA and 30 μM for clostridial ferredoxin. The apparent Vmax with ferredoxin was about 30 U/mg (at 37°C) with a pH optimum of approximately 7. The temperature optimum was approximately 60°C and the Arrhenius activation energy was 40 kJ/mol (between 30°C and 60°C). The enzyme was extremely oxygen sensitive, losing 90% of its activity upon exposure to air for 1 h at 0°C. Sodium nitrite inhibited the enzyme with a Ki, of about 10 mM. The native enzyme had an apparent molecular mass of approximately 130 kDa and was composed of four different subunits with apparent molecular masses of 48, 30, 25, and 15 kDa which indicates that the enzyme has an αβγδ structure. The enzyme contained 1 mol/mol thiamine diphosphate, and about 12 mol/mol each of non-heme iron and acid-labile sulfur. FAD, FMN and lipoic acid were not found. The N-terminal amino acid sequences of the four subunits were determined. The sequence of the α-subunit was similar to the N-terminal amino acid sequence of the α-subunit of the heterotetrameric pyruvate: ferredoxin oxidoreductases of the hyperthermophiles Archaeoglobus fulgidus, Pyrococcus furiosus and Thermotoga maritima and of the mesophile Helicobacter pylori, and to the N-terminal amino acid sequence of the homodimeric pyruvate: ferredoxin oxidoreductase from proteobacteria and from cyanobacteria. No sequence similarities were found, however, between the α-subunit of the M. barkeri enzyme and the heterodimeric pyruvate: ferredoxin oxidoreductase of the archaeon Halobacterium halobium.
46 citations
TL;DR: Cell extracts prepared from Methanosarcina barkeri converted acetate into methane and carbon dioxide under a hydrogen atmosphere in a manner consistent with that observed in whole cells and a proposed model for ATP generation from acetate that involves both membrane-bound and soluble enzymatic components such as CO dehydrogenase.
Abstract: Cell extracts prepared from Methanosarcina barkeri converted acetate into methane and carbon dioxide under a hydrogen atmosphere. Methanogenesis by cell extracts required acetate and ATP and, the in vitro rate was 5 to 10% of the rate of methanogenesis observed during exponential growth of cells on acetate. Methane and carbon dioxide produced by cell extracts originated predominantly from the methyl and carboxyl groups of acetate, respectively, in a manner consistent with that observed in whole cells. Acetate degradation activity was detected in the soluble (150000 × g supernatant) fraction and not in the membrane fraction. These results are discussed in relation to a proposed model for ATP generation from acetate that involves both membrane-bound and soluble enzymatic components such as CO dehydrogenase.
46 citations
TL;DR: It is shown that CO2 rather than HCO3- is the active species of 'CO2' utilized by the dehydrogenase, and results are consistent with N-carboxymethan ofuran being an intermediate in CO2 reduction to formylmethanofuran.
Abstract: Formylmethanofuran dehydrogenase from methanogenic Archaea catalyzes the reversible conversion of CO2 and methanofuran to formylmethanofuran, which is an intermediate in methanogenesis from CO2 a biological process yielding approximately 0.3 billion tons of CH4 per year. With the enzyme from Methanosarcina barkeri, it is shown that CO2 rather than HCO3 is the active species of ‘CO2’ utilized by the dehydrogenase. Evidence is also presented that the enzyme catalyzes a methanofuran-dependent exchange between CO2 and the formyl group of formylmethanofuran. The results are consistent with N-carboxymethanofuran being an intermediate in CO2 reduction to formylmethanofuran.
46 citations